I got my lawn mower out this week and started it one time and it started smoking. I went to check the oil and it was full of gas and gas also spit out the exhaust.

The OIL BREATHER needs to be replaced. Usually a funky thing mounted in the crankcase with a tube going nowhere. Depends on engine.

Something else you might check for is dirt and debri in bottom of carb,gets under inlet needle gas will go through the intake valve and fill the engine block,Don't run with this in it.could be bad.
Luck